Tests for Diabetes During Pregnancy - Choosing the right Glucose Tolerance Test for Pregnancy

Glucose Tolerance tests or Glucose Challenge tests during pregnancy are commonly done to test for chances of Gestational Diabetes Mellitus. This is a condition in which the mother's sugar values are higher than a given threshold. While Gestational Diabetes Mellitus, usually doesnt harm the mother, it can affect the developing fetus. This article explores the different types of Glucose Tolerance Tests during pregnancy, their normal ranges, and the advantages of one over the other.

Published Date : 2024-02-20T06:09:25.910Z

Updated Date : 2024-02-20T18:09:34.420Z

Why are sugar levels tested during pregnancy?

Pregnancy is associated with many changes in the mother's body. One of these changes is the reduced sensitivity of the body to insulin. Insulin normally causes sugar to move from your blood into the different cells and organs of your body. This causes your blood sugar level to fall.

During pregnancy, especially towards the end of the 5th month, there is a reduction in the sensitivity of your cells and organs to insulin

.

In effect, your blood sugar level rises, as the cells don't respond well to the insulin already in your blood. This causes diabetes.

What causes the mother's body to resist insulin?

There are a vareity of factors at play during pregnancy, which reduce insulin sensitivity. These include

1. The junction between the mother and the developing baby is called the placenta, and it secretes various hormones that alter insulin sensitivity in the mother
.
2. During pregnancy, the mothers body secretes increasing levels of different hormones like oestrogen, and also steroid hormones.

These and several other factors, like the increased weight, increased blood volume and blood pressure may also contrinbute to insulin sensitivity.

Does this reduced ability to metabolize glucose affect all mothers?

Yes, to some extent, insulin resistance develops in all mothers. The extent to which this develops differs and hence it is important to check for glucose levels being out of range.

How is sugar or glucose tested during pregnancy?

Glucose is usually tested between weeks 24-28. This is the time associated with the onset of insulin resistance. As such it is the best time to catch elevated sugar levels. Tests for sugar during pregnancy are different from normal blood sugar tests, in that, they are usually done only after giving you a specific and fixed amount of glucose, and testing your sugar after a predetermined period of time.

Why is it called a Glucose Tolerance or Challenge Test?

Tolerance or Challenge are words used to explain the fact that we give the body a fixed/known amount of glucose, and then see how well it metabolizes the same.

How are these tests done?

In virtually every variation of these tests, you will be asked to fast overnight or for 8=12 hours. Following the fast, you are asked to consume a fixed/known amount of glucose. This can vary depending on the type of test being performed from 00 gm to 100 gm. Before taking the glucose a fasting blood sugar sample is collected. After a fixed duration of time post the glucose administration another sample of blood is collected, and these values are compared to known cutoffs.

Which are the different types of Glucose Tolerance Tests ?

There are 4 major Glucose Tolerance tests that have been described by major organizations. We enlist each with its variations.

WHO Method - 2 samples spaced 2 hours apart

In this method, you are asked to fast for 10-12 hours. A fasting blood sample is collected. You are then given 75gms of a sugar solution. The second sample is collected after 2 hours. The normal ranges for this test are as follows:

1. Fasting Sugar - Less than 126 mg/dl
2. 2 hour sugar sample - Less than 140 mg/dl

If either of the 2 values are above the cutoffs, the patient is considered to be positive for Gestational DIabetes Mellitus.

IADPSG - International Association of DIabetes and Pregnancy Study Group Method - 3 samples spaced 1 hour apart

In this method, you are asked to fast for 10-12 hours. A fasting blood sample is collected. You are then given 75gms of a sugar solution. The second sample is collected after 1 hour. A third sample is collected after 2 hours. The normal ranges for this test are as follows:

1. Fasting Sugar - Less than 92 mg/dl
2. 1 hour sugar sample - Less than 180 mg/dl
3. 2 hour sugar sample - Less than 152 mg/dl

If 2 of the 3 values are above the cutoffs, the patient is considered to be positive for Gestational DIabetes Mellitus.

DIPSI Method - Single sample 2 hours after standard dose

The DIPSI Method is special in the sense, that you are not required to fast and it can be done at any time. You will be given 75 gm of glucose and a single blood sample is collected after 2 hours. If the sugar value is above 140mg/dl it is considered to be positive for GDM.

American DIabetes Association Method - 4 samples after 100 gm of glucose, spaced 1 hour apart

In this method, you are asked to fast for 10-12 hours. A fasting blood sample is collected. You are then given 100gms of a sugar solution. The second sample is collected after 1 hour. A third sample is collected after 2 hours. And a fourth sample is collected after 3 hours. The normal ranges for this test are as follows:

1. Fasting Sugar - Less than 95 mg/dl
2. 1 hour sugar sample - Less than 180 mg/dl
3. 2 hour sugar sample - Less than 155 mg/dl
4. 3 hour sugar sample - Less than 140 mg/dl

If 2 of the 4 values are above the cutoffs, the patient is considered to be positive for Gestational DIabetes Mellitus.

Which is the best method?

There is no single best method. Each method has its pros and cons. The DIPSI method is easiest to do as you don't need to be fasting and there is only one blood samples. The American DIabetes Association procedure is the most extensive and is more effective in mapping small deviations, since 4 samples are collected.

Which method is done at Pathofast Lab Pune?

At Pathofast, we prefer the IADPSG Method. This is because, it allows good granularity (with 3 samples). At the same time, it starts with a fasting state and so is easier to reproduce.

What about the WHO method?

Several doctors in India, recommend the WHO method. This is because there are only 2 blood samples, so it is easier to perform. It is also the same method as is done in non-pregnant women - even the cutoff's are the same as those for non-pregnant individuals. As such it is easier to perform at different centers.

What method should I go for?

The best option is to discuss this with your obstetrician. Doctors often are experienced with interpreting a particular method. If requested, a lab will perform any of the given methods. Go with your doctor's choice. If your doctor does not recommend a specific method, it is best to go with the IADPSG or WHO methods. While the ADA Method is very granular and effective in detecting diabetes, it is cumbersome and 4 blood samples mean 4 pricks and some patients are reluctant to be pricked so many times on one day.